This invention relates to an ink jet image recording apparatus used as an ink jet printer, an ink jet plotter, or the like and an ink jet recording head incorporated therein.
A recording head in a related art adopts a configuration wherein a plurality of pressure generating chambers each having a nozzle orifice are formed side by side, an elongated common ink reservoir is formed along an arrangement direction of the pressure generating chambers, the common ink reservoir and the pressure generating chambers are made to communicate with each other by ink supply channels, each pressure generating chamber is provided with a pressure generating element via a vibration plate, and an ink drop is jetted through the nozzle orifice as the pressure generating element causes pressure fluctuation to occur in the pressure generating chamber. The common ink reservoir has a tapering-off shape with the flow passage width narrowed at left and right end portions at the most distance from an ink supply tube for supplying ink to the common ink reservoir for the purpose of decreasing the cross-sectional area, thereby increasing the flow velocity of ink, thereby eliminating remaining bubbles at the time of filling with ink or at the cleaning time of sucking through the nozzle orifices.
One face of the common ink reservoir is partitioned by an elastic film, thereby giving large compliance for the purposes of absorbing pressure of ink flowing backward from the ink supply channel at the ink jetting time and supplying ink to each pressure generating chamber quickly.
However, with the recording head in the related art, if the pressure generating elements are driven under the same condition, a phenomenon occurs in which the jet characteristic of an ink drop jetted through the nozzle orifice of the pressure generating chamber communicating with the common ink reservoir at the end portion thereof (end portion at a distant from the ink supply tube) differs from the jet characteristic of an ink drop jetted through any other nozzle orifice. It is estimated that such a phenomenon occurs because a pressure loss occurs at the end portion of the common ink reservoir and negative pressure occurs at the entrance of the ink supply channel. To solve the problem, it is considered that the compliance of the common ink reservoir is enlarged, but the end portion of the common ink reservoir needs to be tapered off to enhance the bubble excluding capability and thus it is difficult to simply expand the portion having compliance.
There is a tendency to increase the number of nozzles per row from the requirements of speeding up image record, upsizing of the record target, etc.; however, if a cleaning pump is upsized and the bubble excluding capability is enhanced, the amount of excluded ink increases and thus tapering off the tip of the common ink reservoir is inevitable.
It is therefore an object of the invention to provide an ink jet recording head comprising a plurality of nozzle orifices and enabling the jet characteristics of the nozzle orifices to be made uniform and to provide an image recording apparatus incorporating the above ink jet recording head.
According to the first aspect of the invention, there is provided an ink jet recording head comprising:
a common ink reservoir;
an ink supply passage for supplying ink to the common ink reservoir;
a plurality of cavities arranged in a longitudinal direction of the common ink reservoir, which are to be pressure generating chambers; and
an ink supply channel communicating the common ink reservoir and the respective cavities,
wherein at least one ink supply channel situated in the vicinity of at least one longitudinal end portion of the common ink reservoir has at least one of a different cross-section area and a different length from the other ink supply channels.
According to the second aspect of the invention, in the ink jet recording head of the first aspect, the ink supply passage communicates with the common ink reservoir substantially at the center of the longitudinal direction thereof.
According to the third aspect of the invention, in the ink jet recording head of the first or second aspect, a cross-sectional area of the common ink reservoir is reduced at the end portion thereof.
According to the fourth aspect of the invention, in the ink jet recording head of any of the first to third aspects, vibration damping coefficients of the respective ink supply channels are substantially the same.
According to the fifth aspect of the invention, there is provided an ink jet recording head comprising:
a common ink reservoir in which a cross-sectional area of at least one longitudinal end portion is reduced;
an ink supply passage for supplying ink to the common ink reservoir;
a plurality of cavities arranged in a longitudinal direction of the common ink reservoir, which are to be pressure generating chambers; and
an ink supply channel communicating the common ink reservoir and the respective cavities,
wherein an inertance of at least one ink supply channel situated in the vicinity of the longitudinal end portion of the common ink reservoir is smaller than an inertance of the other ink supply channels.
According to the sixth aspect of the invention, in the recording head of the fifth aspect, the volume of the respective cavities is made constant.
According to the seventh aspect of the invention, there is provided an ink jet recording head comprising:
a common ink reservoir in which a cross-sectional area of at least one longitudinal end portion is reduced;
an ink supply passage for supplying ink to the common ink reservoir;
a plurality of cavities arranged in a longitudinal direction of the common ink reservoir, which are to be pressure generating chambers;
an ink supply channel communicating the common ink reservoir and the respective cavities; and
an hypothetical ink supply channel defined as a sum of the length of the ink supply channel situated in the vicinity of the end portion of the common reservoir and the length from a point where the cross-sectional area of the common ink reservoir is started to be reduced to a point of the ink supply channel communicating with the common ink reservoir,
wherein an inertance of the respective hypothetical ink supply channels is identical with an inertance of the respective other ink supply channels.
According to the eighth aspect of the invention, in the recording head of the seventh aspect, the volume of the respective cavities is made constant.
According to the ninth aspect of the invention, in the ink jet recording head of any of the fifth to eighth aspects, the ink supply channel situated in the vicinity of the end portion of the common ink reservoir has at least one of a different cross-section area and a different length from the other ink supply channels to determine the inertance thereof.
According to the tenth aspect of the invention, in the ink jet recording head of any of the fifth to ninth aspects, the ink supply channels communicate with the associated cavities on an hypothetical line extending in the arrangement direction of the cavities.
According to the eleventh aspect of the invention, in the ink jet recording head of any of the fifth to tenth aspects, the length of the ink supply channel situated in the vicinity of the end portion of the common ink reservoir is reduced. A compliance region of the common ink reservoir in the vicinity of the end portion thereof is expanded in accordance with the reduced amount of the length of the ink supply channel.
According to the twelfth aspect of the invention, in the ink jet recording head of any of the third to eleventh aspects, the cross-sectional area is reduced stepwise.
According to the thirteenth aspect of the invention, in the ink jet recording head of any of the first to twelfth aspects, a partition divides each ink supply channel into a plurality of channels.
According to the fourteenth aspect of the invention, in the ink jet recording head of any of the first to thirteenth aspects, the respective ink supply channels and a part of the respective cavities are divided by a partition wall such that an upper section and a lower section are defined. The divided sections are communicated with each other. At least one of the upper section and the lower section of the ink supply channels are divided by at least one partition into the plural channels.
According to the fifteenth aspect of the invention, in the ink jet recording head of the fourteenth aspect, the partitions provided in the respective upper sections of the ink supply channels are arranged in accordance with positions of piezoelectric elements to be mounted on a top wall of the respective cavities. The partitions provided in the respective lower sections of the ink supply channels are arranged in accordance with the positions of the partitions provided in the upper sections such that the volume of the respective cavities is made constant.
According to the sixteenth aspect of the invention, in the ink jet recording head of the fourteenth of fifteenth aspect, an inertance of the respective upper sections of the ink supply channels and an inertance of the respective lower sections of the ink supply channels are different.
According to the seventeenth aspect of the invention, there is provided an ink jet recording apparatus comprising:
a common ink reservoir;
an ink supply passage for supplying ink to the common ink reservoir;
a plurality of cavities arranged in a longitudinal direction of the common ink reservoir, which are to be pressure generating chambers; and
an ink supply channel communicating the common ink reservoir and the respective cavities;
a nozzle orifice formed in the respective cavities;
a pressure generator for pressurizing the respective pressure generating chambers to eject an ink drop therefrom; and
a controller for generating a drive signal to control the pressure generator,
wherein the speed of the ink drop ejected from the respective nozzle orifices is within xc2x15% of a desired value when the respective pressure generating chambers are pressurized by the pressure generator in accordance with the substantially same drive signal.
According to the eighteenth aspect of the invention, in the ink jet recording head of the seventeenth aspect, at least one ink supply channel situated in the vicinity of at least one longitudinal end portion of the common ink reservoir has at least one of a different cross-section area and a different length from the other ink supply channels.
According to the nineteenth aspect of the invention, there is provided an ink jet recording apparatus comprising an ink jet recording head of any of the first to seventeenth aspects.